Re: [PATCH] sched/fair: Ensure _sum and _avg values stay consistent

[Odin Ugedal]

tor. 1. jul. 2021 kl. 12:34 skrev Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>:
>
> What was HEAD when you checked this? 1c35b07e6d39 was merged in the
> 5.14-rc1 merge window so would not be in 5.13.

>From the kernel log it looks like he used commit dbe69e433722
(somewhere in Linus' tree), and that should include my patch. I don't
think the patches from Vincent in the previous thread have been posted
properly, and I think those can fix the edge case you are seeing.

This should mitigate some issues:
https://lore.kernel.org/lkml/20210622143154.GA804@vingu-book/

while
https://lore.kernel.org/lkml/20210623071935.GA29143@vingu-book/
might also help in some cases as well.

Both of those are needed to make sure that *_avg is zero whenever *_sum is zero.

> # git log v5.13..origin/master --pretty=one | grep 1c35b07e
> 1c35b07e6d3986474e5635be566e7bc79d97c64d sched/fair: Ensure _sum and _avg values stay consistent
>
> It's not tagged for stable and lacks a Fixes: tag so I don't think
> it'll be automatically picked up for 5.13-stable unless Odin sends it
> to stable@xxxxxxxxxxxxxxx.

Ahh, so the "Fixes" tag is what makes them pick it up...  Thanks! I am
fairly new to this, but it does make sense when I think about it. I
have seen https://www.kernel.org/doc/html/v5.13/process/stable-kernel-rules.html
before, so I guess I can send it to them to get it into -stable. The
assertion is not a part of v5.13 either though, so people will not see
this warning there (but it can still cause fairness issues).

> --
> Mel Gorman
> SUSE Labs

Thanks
Odin